Alex, I would have asked on here before ordering anything, I will be looking at a similar sort of size build & had been looking at 20mm supported rail, you sure 16mm will be up to the job? Doubt there is that much difference in price for the difference it might make to the machine. The other thing is do you know what usable Z axis travel you are going to have with a 200mm ballscrew? I know you may think you don't need much for what you intend to cut but our plans have a habit of changing once we realise what else can be done. If you only intend to build one machine then it might be best to make sure you cover all the bases.

Didn't notice at first glance but the other thing is that you only have one ballscrew on each axis. With machines of this sort of size then people would recommend 2 on the longest axis at least to ensure the gantry moves smoothly.